A common problem occurring in the preparation of polymers of conjugated dienes or block copolymers of conjugated dienes and vinyl aromatic hydrocarbons is the removal of gelled polymer from the polymerization reactor following an extended continuous polymerization process. Previous attempts to depolymerize the polymer remaining in the reactor have met with only limited success by employing multi-component metathesis catalysts that require the additional use of ethyl aluminum sequichloride (EASC) and diethyl aluminum chloride (DEAC) or Lewis acids. The use of such compounds leads to polymer cross-linking and to reactor corrosion. Cross-linking quickly increases the molecular weight of a polymer. Such a molecular weight increase adversely affects the goal of molecular weight reduction sought from a depolymerization or degelling reaction. Thus, known metathesis catalyst systems possessing a high Lewis acidity are not useful for polymer weight reduction. Other known metathesis catalysts create environmental or safety problems. Furthermore, the use of any of the prior art metathesis catalysts to depolymerize polymers remaining in reactors necessitates the reconditioning of the reactors prior to their subsequent use.